Negative electrode for nonaqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery using the same

Abstract

Provided is a negative electrode for a non-aqueous electrolyte secondary battery, capable of improving the energy density and the cycle characteristics of the battery without lowering the initial charge/discharge efficiency of the battery. This negative electrode includes a negative electrode active material including a silicon oxide represented by SiOx and carbon material. A proportion of a mass of the silicon oxide relative to a total mass of the silicon oxide and the carbon material: y satisfies 0.03≤y≤0.3. A difference between a theoretical capacity density of the negative electrode active material and a charge capacity density of the negative electrode active material when a cutoff voltage is 5 mV relative to lithium metal: ΔC (mAhg−1) satisfies L=ΔC/100 and 6y≤L≤12y+0.2.

The invention claimed is: 
     
       1. A negative electrode for a non-aqueous electrolyte secondary battery,
 the negative electrode including a negative electrode active material including a silicon oxide represented by SiO x  (0.5≤x<1.5) and a carbon material, 
 a proportion of a mass of the silicon oxide relative to a total mass of the silicon oxide and the carbon material: y satisfying 0.03≤y≤0.3, and 
 a difference between a theoretical capacity density of the negative electrode active material and a charge capacity density of the negative electrode active material when a cutoff voltage is 5 mV relative to lithium metal: ΔC (mAhg −1 ) satisfying L=ΔC/100 and 6y≤L≤12y+0.2, wherein: 
 the negative electrode includes: a negative electrode current collector including a metal foil; and a negative electrode material mixture layer formed on the negative electrode current collector, 
 the negative electrode material mixture layer includes the negative electrode active material, 
 a surface layer portion of the negative electrode includes (i) a lithium-containing oxide and a lithium-containing carbonate or (ii) a lithium nitride compound, and 
 the lithium compound is present in a region having a thickness of 0.1 to 3 μm from a surface of the negative electrode. 
 
     
     
       2. The negative electrode for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein the ΔC is smaller than an irreversible capacity density. 
     
     
       3. The negative electrode for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein the ΔC is larger than an irreversible capacity density. 
     
     
       4. The negative electrode for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein the proportion y satisfies 0.03≤y≤0.15. 
     
     
       5. The negative electrode for a non-aqueous electrolyte secondary battery according to  claim 1 , wherein the negative electrode active material is pre-doped with lithium. 
     
     
       6. A non-aqueous electrolyte secondary battery comprising:
 the negative electrode according to  claim 1 ; 
 a positive electrode capable of electrochemically absorbing and releasing lithium; and 
 a non-aqueous electrolyte.